I've never had so much trouble with a thermostat housing...

Discussion in 'Small Block Tech' started by MrSony, Nov 26, 2018.

  1. MrSony

    MrSony Well-Known Member

    I've "fixed" it over 5 times now. First, replaced the gasket. Then filed the (aluminum) housing flat, it was pitted. Plus another new gasket. Then a new gasket and sealer. Then a steel thermostat housing I had, plus new gasket with sealer. Most recently, a near mint condition steel housing with a gasket, no rtv this time (I guess the ridge on the housing wasn't enough), and it still leaks. Every single part in the cooling system is new, engine is freshly rebuilt last year. This just started happening this month. Was fine for the past year. And the temp gauge will wander from what I think is 210ish back to ~190 (195* stat, which I also changed), over the course of a minute it will do it 3 or 4 times. It's in my '85 Regal with a '70 SP 350. What puzzles me the most, is this just started out of the blue. no warning, nothing. And what infuriates me the most, is nothing I have tried has worked. It will be fine for a day, at most 2, then start leaking again. It is seemingly leaking from the bottom portion of the gasket, I can never see any droplets running down the sides or the top. There is no spray, no dribbles. It also only does it after the car is shut off after being at temp. Temp peaks at 230 when off then comes back down normally.
  2. buick64203

    buick64203 Just plum crazy Staff Member

    Hate to ask a stupid question, but are you sure the t-stat is seated in the groove and didn't fall when you installed the housing? I cant tell you hoe many times this happened to me. You go to put the housing on and the t-stat drops out of its groove. When that happens, it will start leaking on the bottom. I made it a habit now of sticking my finger through the hose opening and pressing the t-stat while I tighten things up

    Aluminum intake or iron? id the stat isn't falling out of its groove, are you sure the stat fits in there properly and isn't hanging over into the gasket surface?
    Mark Demko likes this.
  3. OHC JOE


    Mine has started to leak also.
    I removed it cleaned up the area new gasket .let it sit for a day drove her to work popped open the hood nothing there about four hours later coolant was sitting there ....
  4. TrunkMonkey

    TrunkMonkey Well-Known Member

    Maybe the hose. A lot of clamps (especially worm type) are notorious for creating a pinched spot at the worm gear that seeps.
    (see my cheesy paint cross section of the water neck, hose, clamp and coolant)

    Tuck paper towel around the inside of the hose edge, not touching the gasket area and see if it gets wet.
    Mark Demko, PCUB and MrSony like this.
  5. MrSony

    MrSony Well-Known Member

    Factory cast iron intake. Positive thermostat is in it's groove, and fits nicely. It doesn't poor or squirt, it just seeps. At most it's a teaspoon of coolant at a time. I'll try that paper towel method.
  6. Mike B in SC

    Mike B in SC Well-Known Member

    I thought they were supposed to do that, so you would know that you still had coolant! :^) Mine has been leaking like that since I have owned my 68 GS, about five years. One day I will look at it...
  7. gstewart

    gstewart Well-Known Member

    I had the same leak problem also. I had to file flat the housing surface & the surface on the intake. I found a cork gasket, used sealant on both surfaces and no leaks. That was at least 10 years ago.
  8. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD"

    I have had that off and on, always manage to get it sealed. I find when it does leak, it is always when cold, then the leak stops. When the stat is closed, I'm thinking there is more pressure through the bypass hose. I suggest you pay extra attention to that end of the housing making sure that the surface is absolutely flat. Same for the intake manifold side. I have had good luck with the thicker gasket cements like the Indian Head Gasket Shellac.

  9. Fox's Den

    Fox's Den 22 years of racing the same 355 Buick motor

    My new SP3 was leaking at the bottom of the gasket also I used the Gaskacinch. I had to do it a second time and wouldn't you know it, it started to leak after I shut off the motor. I gave it a little more on the tighten the next day and it finally stopped.

    So what I would do is when you put it back on if you do it again start the car up get it warm then wait till the next day and tighten a little bit and hopefully you will be good. I would use the Indian Head gasket sealer too, it seems to always work the best, it is the sealer that has been around forever.
    Mark Demko likes this.
  10. Mark Demko

    Mark Demko Well-Known Member

    Yah better take that SP3 off then and go back to stock:D
  11. Mart

    Mart '71 350 GS, almost stock

    If I run into the difficulty you're having, I use this stuff.

    Attached Files:

  12. Fox's Den

    Fox's Den 22 years of racing the same 355 Buick motor

    How old is that, as old as you, LOL:D

    It says it is made in USA it has to be at least 20 years old.

    OK Demko I go back to stock, Ha. I even bought a new neck so it would not leak, should have put the old pitted one back on.

    Word on the street has it you ready to rumble.
    Mart and Mark Demko like this.
  13. Jim Blackwood

    Jim Blackwood Well-Known Member

    Might try "Right Stuff" sealant, that works pretty good for problem children. Hard to get back apart though. Make sure both surfaces are absolutely clean and then just go finger tight and cinch it down the next day. That seems to work pretty good most of the time. Could also do a wipe around the neck before the hose goes on. Make sure to get all the antifreeze off of course.

  14. 1987Regal

    1987Regal Well-Known Member

    Mines does that when it gets cold. Usually in storage. spring through summer it doesn't seep
  15. Mark Demko

    Mark Demko Well-Known Member

    2 bbl intake LOL:D
  16. MrSony

    MrSony Well-Known Member

    Did the paper towel trick, confirmed it's not leaking from the hose. Will report back probably this weekend once I can fix it. it's leaking about a teaspoon every time, but i have a jug of 50/50, and it's my only car. So no real time to fix it, especially since I work nights.
  17. Fox's Den

    Fox's Den 22 years of racing the same 355 Buick motor

    It may just seal itself up in a few days hold out a little longer.
  18. TrunkMonkey

    TrunkMonkey Well-Known Member

  19. gstewart

    gstewart Well-Known Member

    I remember my dad using Indian Head gasket sealer (it had a different name back then but same type of sealant) and never had a leak.
    Seems to me that the sealer was shellac based.
    Last edited: Nov 29, 2018
  20. MrSony

    MrSony Well-Known Member

    Been about 2 weeks.

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